FBI investigators have not been able to produce any persuasive evidence that Orlando gunman Omar Mateen was gay or pursuing homosexual relationships, sources say.

The FBI began looking into that possibility after media reports last week quoted men as saying that Omar Mateen had reached out to them on gay dating apps and had frequented the gay nightclub where the June 12 massacre took place.

One man claimed to be Mateen's gay lover, while another recalled Mateen as a regular at the Pulse club who tried to pick up men.

But the officials say the FBI has not found concrete evidence to corroborate such accounts.